1. Field of the Invention
The present invention relates to multi-speed gear transmissions and more particularly, to constant mesh collar shift-type transmissions for large industrial or agricultural vehicles and housings therefor.
2. Description of the Related Art
Transmissions for agricultural and industrial vehicles must provide a wide variety of speeds and ranges to suit different load or draft requirements. Efficient and convenient operation of these vehicles demands that speed changes within a given range be made while the vehicle is moving.
A wide variety of transmissions meet these requirements by using collar shift and/or planetary elements to provide the speeds needed and to allow speed changes within selected gear ratios (ranges) while the vehicle is on the move. U.S. Pat. No. 4,063,464 (Crabb), for example, teaches a heavy-duty collar shift-type transmission having six shafts with collar shift clutches mounted on three of the shafts. The clutches control the interaction of numerous intermeshing gears mounted on the shafts to provide several ranges selectable while at rest and several speeds within each range selectable while moving. U.S. Pat. Nos. 3,654,819 (Link); 3,710,637 (Fisher et al.) and 4,341,127 (Stodt) teach similar transmissions using only four shafts with clutches on three of the shafts. The clutches are sometimes controlled hydraulically, e.g., as taught by Fisher et al., and sometimes by cams, e.g., as taught by U.S. Pat. No. 4,409,858 (Lasoen). Planetary systems sometimes are provided ahead of the collar shift transmission to add additional ranges, e.g., as taught by U.S. Pat. No. 3,774,474 (Recker et al.).
In collar shift arrangements, a main drive clutch generally is used to interrupt power input to the transmission when altering engagement of the collar shift elements. The collar shift elements often consist of synchronizer clutches adapted to couple rotating gear meshes with a synchronously rotating shafts. When the vehicle is in motion, the output portion of the power train has a very large amount of momentum, so that synchronization typically is achieved by altering the speed of the components upstream of the synchronizer to match the speed of the components downstream of the synchronizer. Since synchronizer longevity decreases as the momentum transfer across the synchronizers increases, the life of a synchronizer can be improved by minimizing the number and mass of elements between the main drive clutch and the synchronizer. In many transmission arrangements, synchronizer clutches are not closely coupled to the driven end of the main drive clutch and such arrangements have the disadvantage of decreasing synchronizer life.
Another frequent requirement for large industrial or agricultural equipment is availability of direct mechanical output from the engine to power a variety of service attachments. To fulfill this requirement, a power take-off (PTO) shaft often passes through or receives power from the transmission. It is advantageous to have a transmission through which a PTO may be routed without the addition of extra gear elements.
In addition to mechanical power, most agricultural and industrial equipment uses hydraulic power supplied by a hydraulic pump. The pump and transmission both receive mechanical input from a common power source so it is convenient to locate the gear elements and the pump in close proximity. However, combining the gear elements and the pump into one housing increases the size of the transmission and makes the combined housing less adaptable to a wide variety of applications.
Regardless of the exact structure employed, the long accepted objectives for transmissions are that they be efficient and lightweight. Accordingly, it is desirable to minimize the number of components within the transmission while still allowing a wide range of gear ratios. Reducing the number of components and their complexity also serves to reduce space and generally increases reliability. Furthermore, arranging the transmission to minimize the number of gear meshes between the input and output shafts of the transmission for a given gear ratio increases the overall efficiency.
In addition to the power and gearing requirements, the design of a transmission for a specific application also includes the adaptation of the transmission housing or its surroundings to suit a particular and often size-restricted location on a vehicle. Therefore, it also is desirable to have a transmission housing that is easily adaptable to varying constraints and application locations, and that will allow modification of the speed changes available from the transmission without a major alteration to the housing. U.S. Pat. No. 4,023,439 (Herr) teaches using modular transmission components to this end.